Hexane (C6H14) is Class 2, but Pentane (C5H12) is Class 3...
"SOLVENTS GROUPED BY CLASS
Solvents in Class 1 (Table 1) should not be employed in the manufacture of drug substances, excipients, and drug products because of their unacceptable toxicity or their deleterious environmental effect. However, if their use is unavoidable in order to produce a drug product with a significant therapeutic advance, then their levels should be restricted as shown in Table 1, unless otherwise justified. The solvent 1,1,1-Trichloroethane is included in Table 1 because it is an environmental hazard. The stated limit of 1,500 ppm is based on a review of the safety data.
Solvents in Class 2 (Table 2) should be limited in pharmaceutical products because of their inherent toxicity. PDEs are given to the nearest 0.1 mg/day, and concentrations are given to the nearest 10 ppm. The stated values do not reflect the necessary analytical precision of determination. Precision should be determined as part of the validation of the method.
Solvents in Class 3 (Table 3) may be regarded as less toxic and of lower risk to human health. Class 3 includes no solvent known as a human health hazard at levels normally accepted in pharmaceuticals. However, there are no long-term toxicity or carcinogenicity studies for many of the solvents in Class 3. Available data indicate that they are less toxic in acute or short-term studies and negative in genotoxicity studies. It is considered that amounts of these residual solvents of 50 mg per day or less (corresponding to 5,000 ppm or 0.5 percent under Option 1) would be acceptable without justification. Higher amounts may also be acceptable provided they are realistic in relation to manufacturing capability and good manufacturing practice (GMP)."
http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM073395.pdf
Gray Wolf, "At this point, we move to the Greek alphabet with Pentane, which has five carbons and 12 hydrogen’s, to Hexane with six carbons and 12 hydrogen’s, and Heptane with seven carbons. There are longer chain Simple Alkanes, but they are typically not used for extraction.
Due to Vander Waal forces, as the chains get longer, their boiling points go up, as does the difficulty in purging out their residuals afterwards."
https://skunkpharmresearch.com/simple-alkanes-alcohols-and-ethers/
"Laboratory use
Pentanes are relatively inexpensive and are the most volatile liquid alkanes at room temperature, so they are often used in the laboratory as solvents that can be conveniently and rapidly evaporated. However, because of their nonpolarity and lack of functionality, they dissolve only non-polar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as chlorocarbons, aromatics, and ethers.
They are often used in liquid chromatography."
"Reactions
Like other alkanes, pentanes are largely unreactive at standard room temperature and conditions - however, with sufficient activation energy (i.e. an open flame), they readily oxidize to form carbon dioxide and water:
C5H12 + 8 O2 → 5 CO2 + 6 H2O + heat/ energy"
https://en.wikipedia.org/wiki/Pentane
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